<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<h1>0</h1>
<h2>0</h2>
<script>
//开启定时器  每隔1s  调用一次f方法
setInterval(f,1000);
let count = 0 ;
function f(){
  count++;
  let h=document.querySelector("h1");
  h.innerText=count;
}


let x = 0;
//匿名方法开启定时器
let timer= setInterval(function (){
  x++;
  let h =document.querySelector("h2");
  h.innerText=x;
  if (x>=50){
    //停止定时器
    clearInterval(timer)
  }
},100)

setTimeout(function (){
  x>=50;
},3000)
</script>
</body>
</html>